The present invention relates to phase comparators and more particularly to phase comparator having an output for a matched phase condition or an output for a 180.degree. out-of-phase condition.
Phase comparators, discriminators, and detectors which respond to the phase difference between two signals are not new. Phase detectors which detect the interval between homologous edges of waveforms are disclosed in several prior art patents. One, such as U.S. Pat. No. 3,805,153 to Gallant, develops a voltage proportional to this phase difference. Others such as U.S. Pat. No. 3,599,102 to G. Mous produce pulses whose width is representative of the phase difference between the inputs. Another, U.S. Pat. No. 3,328,688 to Brooks, compares the leading edge of first of the wave signals to the trailing edge of the other and also compares the leading edge of the second signal to the trailing of the edge of the first signal to obtain a rectangular pulse whose width is proportional to the degree of phase difference.
One problem with these prior art patents is their relatively low resistance to perturbations caused by noisy environments. There are several phase detectors which have been proposed such as that disclosed in U.S. Pat. No. 3,764,902 to T. Rodine which attempt to solve this problem; however, their circuitry tends to be quite complex or unsuited for many applications.
There are also many instances, especially in military and industrial applications, when the circuit need only discriminate or detect phase at one point. That is, when the input signals are 180.degree. out-of-phase or in other cases when the signals are exactly in-phase. At all other phase relationships the determination that the two signals are not at that selected phase relationship need only be made. Additionally, it is often necessary that the circuitry be as efficiently designed as possible, considering durability, power requirements, simplicity, and noise immunity.
The present invention utilizes a network which can be readily miniaturized and makes use of both edges of the input waveforms to provide a simple logical output indicative of the selected phase relationship. It also has that capability of being utilized in environments requiring a high degree of noise immunity.